For full portability, similarly on the same tab set the Other settings to Program (XnView).

Although the various program ZIP downloads may be used as portable programs on a memory stick, there may be some detailed limitations: for example, the Ghostscript utility required to view PDF and certain other file formats is only available as an installer, and so cannot be used with a portable copy of XnView software. There may, however, be a PortableApps solution for that at least for XnView (Classic).